Method and composition for platinum plating and articles plated therewith

ABSTRACT

AN ARTIFICIAL TOOTH IS PROVIDED COMPRISING A PORCELAIN BODY CONTAINING A NOBLE METAL OR ALLOY PIN COIL PLATED WITH A CONTINUOUS LAYER OF PLATINUM. THE PIN COIL IS PLATED WITH AN ELECTROLESS PLATINUM PLATING SOLUTION CONSISTING ESSENTIALLY OF: (A) CHLOROPLATINIC ACID; (B) A PLATINUM REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF HYDRAZINE AND SALTS OF HYDRAZINE; (C) HYDROCHLORIC ACID; (D) A WETTING AGENT; AND (E) WATER. THE CONTINUOUS LAYER OF PLATINUM CAN APPROACH A THICKNESS OF ONE MIL.

Feb. 16, c, w, WALTER ETAL 3,562,911

METHOD AND COMPOSITION FOR PLATINUM PLATING AND ARTICLES PLATED THEREWITH Original Filed Oct. 21. 1965' INVENTORS F 16.2 FRANK H. LEAMAN CHARLES w. WALTER United States Patent 3,562,911 METHOD AND COMPOSITION FOR PLATINUM PLATING AND ARTICLES PLATED THEREWITH Charles W. Walter and Frank H. Leaman, York, Pa.,

assignors, by mesne assignments, to Dentsply International Inc., York, Pa., a corporation of Delaware Original application Oct. 21, 1965, Ser. No. 499,661. Divided and this application Dec. 3, 1968, Ser. No. 310,416

Int. Cl. A61c 13/.00 US. Cl. 32-8 6 Claims ABSTRACT OF THE DISCLOSURE An artificial tooth is provided comprising a porcelain body containing a noble metal or alloy pin coil plated with a continuous layer of platinum. The pin coil is plated with an electroless platinum plating solution consisting essentially of:

(a) Chloroplatinic acid;

(b) a platinum reducing agent selected from the group consisting of hydrazine and salts of hydrazine;

(c) hydrochloric acid;

(d) a wetting agent; and

(e) water.

The continuous layer of platinum can approach a thickness of one mil.

This application is a division of application Ser. No. 499,661, filed Oct. 21, 1965, and now abandoned.

The present invention is directed to platinum electroless plating solutions for electroless plating of copper, copper alloys and metals and alloys more noble than copper. This invention is further directed to the electroless plating of pin coils composed of such metals with platinum and to artificial porcelain tooth products containing the platinum plated coils or anchorages. More particularly, the invention relates to an electroless plating solution and process for electroless plating platinum, smoothly and of even thickness (uninterrupted) in substantial, predictable thicknesses, and reasonably free from stress and to the plating of pin anchorages or coils for retaining and affixing pins to porcelain teeth.

Heretofore, substantial thicknesses of platinum could be deposited only by electrodeposition. This electrolytic type of plating, however, has not been found to be capable of providing a completely plated product such as a tiny tooth coil or anchorage. Thus, an even deposit of platinum cannot be produced in depressed areas and in parts that are very small or very complicated in design by the use of prior known electrodeposition techniques. Moreover, the electrodeposition of platinum cannot be employed for the direct application to non-conductive surfaces.

Also, in very limited and special applications, solutions of platinum salts could be used for the immersion plating of platinum on some base metals to several millionths of an inch in thickness. Because of the limited application of such techniques and the inherent disadvantages associated with immersion plating, the use of such system is not generally accepted.

By electroless platinum plating such as contemplated by this invention, however, it is possible to produce an even deposit of platinum even in depressed areas and areas too small or too complicated in design to plate practically by electrodeposition. Electroless plating of platinum also enables direct application of the platinum to properly selected and prepared non-conductive surfaces, such as acrylic resin, epoxy resins, polypropylene, Teflon, etc.

It is therefore a primary object of this invention to provide an electroless plating composition and process for the platinum plating of various materials.

It is a further object of this invention to provide an electroless method of platinum deposition in an autocatalytic manner to enable the continuous build-up of platinum to a pre-determined thickness.

It is yet a further object of this invention to provide a composition and process for the platinum plating of dental pin coils or anchorages of noble metals.

It is yet a further object of this invention to provide artificial porcelain teeth containing platinum deposited noble metal pin coils or anchorages.

Still further objects and advantages of the present invention will become apparent from the following non-detailed description of the invention.

The electroless plating composition of the present invention is composed of the various components characterized as follows:

Stabilizer: The stabilizer that is employed in the bath of the present invention is usually employed in the form of chloride ions. These ions function to stabilize and keep the reduction of platinum under control. For best efficiency, a pH of about .6 is advantageously employed and such can be produced through the use of hydrochloric acid.

Driving force: The driving force or activation of the solution is induced by the employment of a chemical reducer. Hydrazine dihydrochloride has been found preferable for this purpose; however, hydrazine itself or other hydrazine salts, e.g., hydazine sulfate, etc., may be employed to reduce the Chloroplatinic acid to pure platinum metal.

Plating material: Chloroplatinic acid is reduced by the driving force (hydrazine or salt of hydrazine) to produce pure platinum metal which deposits upon the object to be plated.

Wetting agent: The function of the wetting agent in the plating bath of the present invention is to even out the plated coating, i.e., to promote a uniform thickness of pure platinum metal on the entire surface of the object to be plated. For this purpose, sulfosalicylic acid is preferred. Other suitable wetting agents for the purposes of this invention include ethanol and benzene sulfonic acid.

For the practice of this invention, it is advantageous to maintain the composition of the bath components within the following range of concentration in the aqueous bath:

Constituent: Moles per liter Platinum (chloroplatinic acid) 0.00050.0625

Hydrazine or hydrazine salts 0.0030.25 Hydrochloric acid (chloride ion) 0.02-5.0 Sulfosalicylic acid (wetting agent) 0.0005-0.025

In addition to the main bath constituents set forth above, various other salts may be added to improve bath stability and plating efiiciency, and also contribute to stress reduction in the deposited metal in some instances. The following salts and similarly acting materials are beneficial generally within the following range of concentration: hydrazine benzenesulfonic acid, 10-200 p.p.m.; benzenesulfonic acid, 6-1200 p.p.m.; and 2,7-naphthalene disulfonic acid disodium salt, 5400 p.p.m. It is apparent that the invention herein described is not restricted to one particular plating solution, but is inclusive of many distinct and separate baths of different platinum, chloride ion, and hydrazine concentrations.

The total reaction for the chemical deposition of platinum is illustrated as follows:

7 Half reactions showing electron exchange are as follows:

The bath becomes more acid during plating and is less likely to decompose. Initial excess of chloride ion prevents spontaneous bath decomposition by keeping the reaction in Equation 1 from taking place too rapidly. The chloride ion serves as a stabilizing agent in the bath so platinum can be deposited at a controlled rate. Heat drives the reaction to completion. A temperature of 60 C. to 70 C. is generally necessary for the most efficient bath operation of properly balanced plating solutions, which may reach a plating efficiency of 99%. Deposited platinum catalyzes the reaction so as to enable continuous plating of platinum.

Platinum deposition generally continues for about 20- 40 minutes depending on the bath temperature, the surface area being plated, the amount of platinum in solution, and the degree of agitation provided. After the above-stated time the platinum in solution is depleted and the plated objects may be removed. Parts may be platinum plated 'With a relatively stress-free plate without agitation in these baths to a thickness of 0.0003 of an inch. By the use of agitation or tumbling of the parts, bright and adherent plates of platinum 0.0006 of an inch in thickness can be plated in one bath operation. For greater platinum deposits, it is usually advantageous to place the plated parts in a fresh bath and resume platinum build-up on the platinum previously deposited.

Plating solutions with properly equated constituents have the decided advantage of indefinite storage in the form of concentrated platinum solutions of various platinum concentrations, when prepared with the exclusion of hydrazine or its salts used as reducing agents in the active bath. When desired for use, the necessary amount of reducing agent and diluting agent are added to the properly selected platinum stock solution to form an active bath. This fresh starting solution should be used for maximum bath eflicie'ncy in a one shot plating operation to the depletion of platinum in solution shortly after the bath has been prepared. If plating of platinum is interrupted and the solution is cooled and stored, spontaneous decomposition of the bath will not occur and deposition of platinum may be resumed at a later time, but with considerably decreased efficiency. Hydrazine and its salts in aqueous solution undergo hydrolysis and slowly lose their power of reduction, so stored solution containing reducing agents exhibit a loss in efiiciency.

When platinum plating copper and metals less noble than copper, as well as alloys including large amounts of copper such as German silver by the process of this invention, a substantial coating of some noble metal which Will catalyze the reduction of platinum from chloroplatinic acid solution by hydrazine, such as gold, is required prior to the electroless plating of platinum.

For the plating of noble metals, palladium or its alloys, for example, a stress-free, adherent, uniform deposit can be easily produced by utilization of the composition and process of the present invention.

Also, as stated previously, the process of the present invention can be advantageously employed for the direct application of the platinum to properly selected and prepared non-conductive surfaces.

The production of relatively stress-free, adherent, and uniform deposits of platinum in uninterrupted and substantial thickness; by the employment of the bath of the process of the present invention is found to have particular utility in the coating of dental pins and pin coil anchorages.

It is well known to produce pin coils or anchorages for artificial porcelain teeth from noble metals and alloys.

Note, for example, U.S. Pat. No. 2,310,732 to Dietz and U.S. Pat. No. 2,766,527 to Vines et al.

Although the use of palladium for tooth anchorages is desirable from a cost standpoint as compared with other noble metals, i.e., gold and platinum, it has been known for many years that palladium, when subjected to a vacuum firing process, such as comprises the subject matter of U.S. Pat. No. 2,597,469, vaporizes and produces a shade change resulting from the porcelain assuming an uncontrolled and undesirable increase in gray shade in the region surrounding the pin coil, thus decreasing the esthetic nature of the artificial tooth product.

In accordance with the present invention, it has now been found that these small pin anchorages or coils can be easily platinized by the composition and process of the present invention and such anchorages having stressfree adherent, and uniform deposits of platinum, do not oxidize 0r tend to appreciably darken the porcelain tooth upon firing of the raw biscuit and thus the esthetics of the porcelain tooth are preserved.

The necessity to produce a completely covered high palladium content tooth coil is extremely important in view of the advent of new vacuum firing procedures. This primarily is because lowering of the atmospheric pressure during the high fusing temperature more acutely causes a tendency for the palladium or other noble base metal to vaporize through the unplated areas, oxidize, and thereby darken the teeth, than when teeth are fired under normal atmospheric pressure conditions. Although all noble metals, including platinum, tend to vaporize and discolor porcelain teeth slightly during normal firing conditions, as well as under vacuum firing conditions, platinum offends in this matter the least of any of the noble metals.

Details of teeth including anchorages attached thereto are more fully described in the following specification and illustrated in the accompanying drawing forming a part thereof.

In the drawing:

FIG. 1 is a vertical sectional elevation of an exemplary anterior tooth, taken on a plane extending labiallingually and showing an anchorage within a porcelain tooth and a pin soldered thereto.

FIG. 2 is an enlarged View of this same section.

FIG. 3 is a still further enlarged view of the anchorage or coil embedded in a porcelain tooth illustrating the platinum coating and soldering of a dental pin.

FIG. 4 is a perspective view of a suitable dental pin coil anchorage.

In these figures, like numeral represent like components Porcelain artificial teeth, such as the one indicated and illustrated in vertical longitudinal section in FIG. 1 are formed in suitable molds which incidentally are provided with means to facilitate the placing of platinum coated anchorage within the tooth. Various types of molds are suitable for this purpose, one well known type being illustrated in U.S. Pat. No. 1,547,643 to Clapp, dated July 28, 1925. The molds usually comprise at least two separable mold parts which cooperate to define a suitable cavity within which a tooth .10 is molded.

A quantity of raw tooth dough, which has a putty-like consistency and includes porcelain components such as pulverized feldspar and organic binding agents, is intro duced into the mold cavity and surrounds the anchorage 12 on the end of a post. The raw tooth dough is forced into firm engagement with the outer surfaces of anchorage 12 and the molded raw tooth while still in the mold parts, usually is baked while it remains in these parts for a period of time and at a sufiicient temperature, of about 400 F. to remove the moisture from the molded raw tooth and render it sufliciently hard that it might be handled without danger of fracture or being misshapened.

After such preliminary baking, which is not accomplished at sufficiently high a temperature as to fuse the porcelain components, the raw molded tooth or biscuit, as it is known in the artificial tooth field, is placed on a suitable holder resistant to high temperatures and then transferred to a firing furnace where the raw biscuit is fused so as first to burn off the binding material, if used, and then unite the porcelain particles to each other so as to render the tooth 10 substantially homogeneous and solid. Fusing temperatures vary in accordance with the porcelain composition but, in general, range from about 2150 F. to about 2300 F. Such fusing of the porcelain particles also causes the tooth 10 to be fused to the anchorage 12. It also will be noted from the various figures that the exemplary anchorage is provided with an annular flange 16 which fixedly positions the anchorage within the body interior of the tooth 10.

After removal of the post which positions the anchorage or coil #12 in the new dough, the pin 22 is then soldered to the coil or anchorage by means of conventional silver solder 32. In some instances, the soldering of the pin 22 to the coil or anchorage 12 has been found to have the effect of dissolving the platinum plate on the soldered side of the coated component but this in no way affects the asthetics of the porcelain tooth. The platinum coating on the coil or anchorage 12 is represented by numeral 16. By the process of the present invention, thicknesses approaching 1 mil have been capable of being produced.

Either substantially pure palladium or high palladium content alloys are preferred to form anchorages in accordance with the present invention, one reason being the economic factor of price as compared with other noble metals, it being understood that usually only noble metals are satisfactory for such purposes. However, another factor favoring the use of this type of anchorage is the fact that palladium is more compatible with feldspathic porcelain, in that it has a coefficient of expansion nearer that of porcelain than the high gold alloys. If desired to render the anchorage harder than that afforded by substantially pure palladium, suitable small quantities of base metals such as nickel, cobalt, etc., as well as noble metals such as silver, gold, platinum, iridium, rhodium, ruthenium and osmium, might be alloyed with the palladium. Alloys which have been found desirable and operable in accordance with the present invention, in addition to using substantially pure palladium are set forth in the following table:

Number 1, Number 2, Number 3,

percent percent percent Palladimn. 90 85. 5 80 Silver 5 2. 5 Gold 5 12. 0 20 EMMPLE I To make 25 cc. of 1 g./l. platinum plating solution, 0.5 cc. of hydrochloric acid and 0.05 gram of sulfosalicyclic acid were added to 12 cc. of chloroplatinic acid solution containing 0.15 gram of hydrazine sulfate. Bath component concentrations were as follows: 0.026 m.p.l. platinum or chloroplatinic acid, 0.9 m.p.l. hydrochloric acid, 0.045 m.p.l. hydrazine sulfate, and 0.008 m.p.l. sulfosalicylic acid. Small palladium components, i.e., dental pin coils, weighing 3.0001 grams were plated in this solution. The components were tumbled at 14 rpm. in the solution which was held in a glass container and warmed by a hot water bath. Chemical deposition of platinum began at 63 C. and continued for 12 minutes to a final temperature of 70 C. The platinum plated components weighed 3.1224

grams after plating. The deposit had a minimum thickness of 0.15 mil. The plate was dense, adherent, and uniformly deposited, Bath efficiency was 97.9%.

EXAMPLE II To prepare 25 cc. of 2.5 g./l. platinum plating solution containing 5 g./l. platinum, 40 cc./l. hydrochloric acid, and 4 g./l. sulfosalicylic acid was added to a solution of 0.1025 gram of hydrazine dihydrochloride dissolved in 12.5 cc. of distilled water. Bath component concentrations were as follows: 0.0128 m.p.l. platinum, 0.9 m.p.l. hydrochloric acid, 0.04 m.p.l. hydrazine dihydrochloride, and 0.008 m.p.l. sulfosalicylic acid. Some 2.3015 grams of palladium plated dental pins were plated in this solution. Deposition of platinum occurred for 33 minutes at 66 C.-70 C. The plated pins weighed 2.3584 grams. Bath efficiency was 91%. The platinum plate was 0.30 mil thick.

EXAMPLE III A platinum plating bath containing 0.0515 m.p.l. or 10 g./l. platinum, 0.1525 m.p.l. hydrazine dihydrochloride, and 0.008 m.p.l. sulfosalicylic acid was prepared. The chloroplatinic acid solution used was prepared from salt that contained excess hydrochloric acid desired for stability in the active bath. Some 12.5 cc. of this bath was used to plate 4.3009 grams of palladium components, i.e., dental pin coils, having a very large surface area to weight ratio. Deposition of the platinum occurred for 17 minutes at 62 C.65 C. The components weighed 4.4155 grams after plating. Bath efficiency was 91.7%.

EXAMPLE IV A platinum plating solution containing 0.026 m.p.l. platinum, 0.81 m.p.l. hydrochloric acid, 0.046 m.p.l. hydrazine dihydrochloride, 0.008 m.p.l. or 0.2 percent sulfosalicylic acid, 0.1 percent or 1000 ppm. benzenesulfonic acid, and 1000 ppm, p-hydrazinobenzene sulfonic acid was prepared, the pH of this solution was 0.6. Palladium, gold, silver alloy dental pin coils weighing 3.0006 grams prior to plating were plated in 25 cc. of this solution. Deposition of platinum began at 67 C. and continued for 12 minutes. A temperature range of 66 C.68 C. was maintained during the plating of platinum. The plated components weighed 3.1246 grams. Bath efiiciency was 99.2%. The average thickness of plate was 0.30 mil.

EXAMPLE V A platinum plating solution similar to that used in Example II, except for the addition of 100 ppm. or 0.01 percent 2,7-naphthalene-disulfonic acid disodium salt, was prepared. Some 3.0027 grams of gold plated dental pins were plated in 25 cc. of this bath. The pins were plated for 30 minutes at 67 C.71 C. to a finished weight of 3.0609 grams. The platinum plate was 0.15 mil thick. Bath efficiency was 93. 1%.

EXAMPLE VI A platinum plating solution containing 1 g./l. or 0.005 m.p.l. platinum, 1.1 m.p.l. hydrochloric acid, and 0.035 m.p.l. hydrazine was prepared by adding 50 cc. of dis tilled water containing 0.23 cc. of 50 percent hydrazine solution to 50 cc. of chloroplatinic acid solution containing 2 g./l. platinum and 2 cc. of hydrochloric acid. These solutions were mixed at room temperature to make an active bath. A foil of 18K gold 2 x 1" x 0.0018 weighing 1.1493 grams was plated in this solution. Deposition of platinum occurred for 15 minutes at 71 C.73 C., at which time the bath began to decompose. The plated foil weighed 1.1853 grams. Bath efficiency was 36%. The platinum plate was millionths of an inch in thickness.

EXAMPLE VII A platinum plating solution of 0.026 m.p.l. platinum, 0.9 m.p.l. hydrochloric acid, 0.046 m.p.l. hydrazine sulfate, and 0.5 percent ethanol was prepared. Gold plated dental pins weighing 8.500 ounces were plated in 1800 cc. of this solution. The plastic container was tumbled at 6 r.p.m. in a hot water bath. Deposition of platinum began at 56 C. The plated pins Weighed 8.764 ounces. Bath efficiency was 91.2%. The thickness of platinum Was 0.40 mil. Other trials have shown that greater solution agitation sharply reduces the plating time for large trials.

EXAMPLE VIII A platinum plating solution of 0.026 m.p.l. platinum, 0.023 m.p.l. hydrazine sulfate, and no additional hydrochloric acid other than that necessary to stabilize the chloroplatinic acid salt from which the chloroplatinic acid solution was made, was prepared. The pH of this solution was 3.4. Gold plated dental pins weighing 4.0125 grams were plated in 25 cc. of this solution at 39 C.45 C. for 9 minutes, at which time the bath decomposed. The pins weighed 4.0530 grams after plating. Bath efficiency was 65%.

EXAMPLE IX A platinum plating solution containing 0.0026 m.p.l. or 0.5 g./l. platinum, 3.5 m.p.l. hydrochloric acid, 0.033 m.p.l. hydrazine dihydrochloride, and 0.008 m.p.l. sulfosalicylic acid was prepared. Two annealed platinum foils measuring 1 x 0.25" x 0.001" weighing 0.2002 gram were plated in 25 cc. of this solution for 65 minutes at 88 C. The pH of this solution was about 0.1. The foils weighed 0.2107 gram after plating. Bath efficiency was 84%. The platinum plate was 90 millionths of an inch in thickness. The plate was dense, adherent, and evenly deposited.

EXAMPLE X A sheet of polypropylene 1.25 square inches in surface area that was properly cleaned, roughened, sensitized and activated was plated in cc. of plating solution like that used in Example IV. The plastic was plated for 6 minutes at 70 C. The plastic gained 0.0295 gram of platinum plate. The thickness of the platinum plate was 70 millionths of an inch.

EXAMPLE XII A sheet of cycolac 1.8 square inches in surface area was plated in 25 cc. of solution like that used in Example IV. The ABS plastic was plated for 8 minutes at 73 C.- 78 C. The plastic gained 0.0667 gram of platinum. The thickness of the plate was 0.11 mil. The platinum deposit was adherent, attractive and uniformly deposited.

EXAMPLE XIII Exactly 2.996 grams of palladium, gold, silver, alloy dental pins were cleaned, annealed, and Water-quenched. Then they were plated in 25 cc. of plating solution like that used in Example IV for minutes at 63 C.67 C. The platinum plated pins weighed 3.0998 grams. Both efficiency was 80%. Photographs of mounted samples showed the platinum plate as a continual uniform deposit 0.75 mil thick.

The following examples illustrate the advantageous use of the platinized dental pin coils or anchorages of the present invention in porcelain tooth products. Again, these examples are illustrative of various embodiments of the present invention and are in no way to be deemed limitative thereof.

EXAMPLE XIV Platinized dental pin coils produced in Example IV are inserted in conventional raw porcelain dough and fired under vacuum atmosphere conditions, such as covered by U.S. Pat. No. 2,597,469, at a temperature of about 2300 F. An examination of the teeth so produced shows no appreciable color change of the teeth, indicating no substantial vaporization or oxidation of the palladium anchorage.

EXAMPLE XV Platinized pin coils of palladium-20% gold alloy were inserted in conventional raw porcelain dough and fired under vacuum at a temperature of about 2300 F. Again, an examination of the artificial teeth so produced shows no appreciable color change.

While certain desired embodiments have been illustrated by way of example, with respect to both dental pins and pin coils, it is to be understood that the invention is not limited to those embodiments and is particularly beneficial in the plating of dental pin coils because of the irregular surfaces thereof. Further, the invention set forth in the foregoing specification is not to be regarded as limited to the specific examples set forth therein, but is to be regarded as broadly as any and all equivalents thereof.

We claim:

1. An artificial tooth comprising a porcelain body having therein a noble metal or alloy pin coil plated with a continuous layer of platinum after fabrication of said pin coil, said pin coil bein plated with an electroless platinum plating solution consisting essentially of:

(a) chloroplatinic acid;

(b) a platinum reducing agent selected from the group consisting of hydrazine and salts of hydrazine;

(c) hydrochloric acid;

((1) a wetting agent; and

(e) water.

2. The artificial tooth of claim 1 wherein in said electroless platinum plating solution components (a), (b), (c) and (d) are present in concentration ranges of 0.005- 0.0625 mole per liter, 0.0030.25 mole per liter, 0.025.0 moles per liter and 0.0050.025 mole per liter, respectively.

3. The artificial tooth of claim 2 wherein said electroless platinum plating solution is further characterized in having a pH of from about 0.1 to about 5.0.

4. The artificial tooth of claim 2 wherein said electroless platinum plating solution additionally contains a stress reducing component selected from the group consisting of hydrazine benzenesulfonic acid and 2,7-naphthalene disulfonic acid disodium salt.

5. The artificial tooth of claim 2 wherein said continuous layer of platinum approaches a thickness of 1 mil.

6. The artificial tooth of claim 2 wherein the pin coil consists essentially of palladium.

References Cited UNITED STATES PATENTS 2,169,731 8/1939 Lease 328 2,310,732 2/1943 Dietz 32-8 2,766,527 10/1956 Vines et al. 328

ROBERT PESHOCK, Primary Examiner 

